(1) Field of the Invention
This invention relates to a reaction injection molding method.
(2) Description of the Prior Art
A reaction injection molding method, namely, a method for obtaining a molded article of a plastic material such as nylon, unsaturated polyester, epoxy or polyurethane by injecting a highly reactive liquid starting material into a mold and effecting polymerization and molding in the mold. In this reaction injection molding method, at least two highly reactive liquid starting materials are ordinarily mixed together by causing them to impinge against each other in a mixing head and then injected into a mold. However, since air bubbles are involved in the starting materials when they are mixed together by impingement, these bubbles are readily left within the resulting molded article. Furthermore, since the liquid starting material is polymerized and molded in the mold, the density varies during the polymerization or the polymerization reaction is advanced non-uniformly, with the result that the surface smoothness of the obtained molded article is readily degraded.